The lung epithelium of mammals is known to contain neuroendocrine-like cells and neuroepithelial bodies. Dense-cored or neuroendocrine-type granules have been previously identified in both of these structures. We are attempting to identify known polypeptide hormones in the normal and neoplastic lung epithelium of various species. Although no corticotropin immunoreactivity was identified in normal lungs by immunohistochemical methods, this hormone was identified in cultured cells obtained from hamsters treated with diethylnitrosamine. These cells were also argyrophilic and contained numerous dense-cored vesicles - these properties have also been observed in human bronchial carcinoids and in some human small cell carcinomas. These results contrast with those obtained with chemically induced rodent squamous cell carcinomas. Such tumors exhibited neither immunohistochemical evidence for corticotropin nor cells containing dense-cored vesicles. We are presently investigating the regeneration of tracheal epithelial cells in order to identify pluripotent or progenitor cells for lung neuroendocrine cells and related neoplasias.